A rotor for an eccentric screw pump or eccentric screw motor produced by cold deformation is disclosed in DE 198 52 380 A1. The pump or motor of this reference has a stator with a continuous helical opening over which the rotor rolls during displacement operation. The stator comprises a cylindrical tube provided with an elastomeric cladding. The elastomeric cladding defines the wall of the passage opening and acts as a seal relative to the stator.
The stator includes a core element and a shell formed around the core element. Beginning with a cylindrical tube, the shell is deformed into a helical configuration. The originally cylindrically shaped tube acquires not only the helical configuration, which is required for the rotor, but this deformation also firmly connects the tube to the core element. In the final state, the thread valleys of the shell of the stator form a tight firm friction fit with the core element. To improve the driving effect between the core element and the shell of the stator, the support element also can be provided with longitudinal ribs.
This prior art rotor can be produced in a cost effective manner in very large numbers. Lengths of up to 6 meters can be reached easily without requiring final machining of the surface of the stator. The surface of the rotor is very smooth and sufficiently stable in its dimensions. The core element present in the shell prevents the rotor from uncoiling when exposed to pressure. Uncoiling of the rotor could lead to a pitch error between the stator and rotor that would result in leaks.
This prior art rotor is made of a steel material that does not have sufficient wear strength for many applications, and also does not have sufficient corrosion-resistance for some applications. In other words, the rotor does not have sufficient erosion resistance. Erosion is understood to mean not only wear by corrosion, but also ablation by sliding abrasion of the transported material on the surface.
It is also known from the prior art to provide the stator with a shell that has a helical configuration similar to the helical configuration of the passage opening. With such stators, the elastomeric cladding, which again serves as sealing material, has an almost constant wall thickness. Larger pressures, or larger torques in the case of an eccentric screw motor, can be produced with such stators.